Three clips of an orange 718 GT4 RS. The first is 25 seconds on a workshop lift, camera panning from the rear bumper down under the car to show the new catless downpipe and the centre-exit tips. The second and third are dusk, filmed from a chase car on an elevated road, the GT4 RS pulling alongside and pulling away. That is the whole set. It is not much. But it is enough to make one argument clearly, which is that this engine is the reason the car sounds good, and the tailpipe is only the messenger.
Why the flat-six is the whole point
The GT4 RS uses the 4.0-litre flat-six taken straight from the 911 GT3 RS and 911 RSR — naturally aspirated, 500 PS, 9,000 rpm, 450 Nm, sitting right behind your head in a mid-engined car. Nothing about it is softened. There is no turbo to flatten the exhaust pulse, no V6 sub-harmonic lope to lean on, no big low-frequency rumble doing the work. Six cylinders fire in two banks of three, evenly, like a metronome, and they run all the way to 9,000 rpm.
That last number is what decides the whole question. At 9,000 rpm a flat-six is producing exhaust pulses at roughly three times the frequency it produces at idle. The top octave is not decoration on this engine — it is a large share of the sound. This is a car whose factory tailpipes are titanium, styled after the 935 Motorsport pipes from 1978. Porsche did not spend a heritage reference on a material choice by accident.
On the 991 GT3 we point people at titanium for the same reason. On a V10 we point them at stainless, because ten cylinders already build a dense low-mid wall and a thin wall would hollow it out. This engine is on the other side of that line: it is a high-revving, high-frequency, weight-obsessed flat-six in a car built around a 1,300 kg target. Thin, stiff, light walls are exactly what it wants.
We measured all three clips. Overall mean levels run from -23.9 dB in the quiet workshop clip up to -12.9 dB in the loudest chase-cam moment, with a peak of -0.7 dB — the phone was clipping at the loudest instant. The 100–800 Hz band sits within 1.5 to 4.2 dB of the overall level across all three. Below 100 Hz is 9.7 to 16.4 dB down. Above 2 kHz is 11.8 to 21.1 dB down.
Read that last number honestly: these clips are quiet on 2 kHz and up. That is not proof the car lacks top end — it is mostly the phone microphone, the workshop ceiling, and the fact that nobody revved a 9,000 rpm flat-six to the limiter in a residential workshop. A flat-six at full throttle makes most of its character above 3 kHz, and a phone pointed at a rear bumper from ten metres away will not capture it. Treat the high-end figures as the phone's ceiling, not the engine's.
What the three clips actually show
The workshop clip is the useful one. The car sits on a two-post lift with the rear wheels hanging free, and the camera walks from the tail down to the underside. You can see the rear diffuser, the two centre-exit tips, the underbody paneling, and the new pipe running forward from the header area. The Korean number plate has been pixelated.
What you cannot do with this clip is hear the engine properly. The microphone is close to the underbody, not the exhaust outlet, the car is cold, and most of the clip is the camera moving rather than the car running. That is why the mean level here is 16 dB below the loudest chase clip. This is a hardware record, not a sound record.
The two chase clips are the opposite problem. Here the car is genuinely loud — the peak hits -0.7 dB, which means the recorder was at its limit — and the flat-six at high revs in a mid-engined car is genuinely hard to ignore. But you are hearing it through a car windscreen, at speed, with traffic and wind and road surface noise underneath it. The 100–800 Hz band is only 4.2 dB below the overall mean here, so the mid-range is carrying the note, which is exactly what a flat-six at a steady high rev does.
We will be straight about the limits again. Three phone clips, two of them from a moving car, none of them a microphone on a tripod, none of them a dyno. They tell you the car is loud, the mid-range is where the character lives, and the hardware underneath is a proper catless downpipe setup. They do not tell you what the system sounds like at 8,500 rpm on a dyno. For that, bring it to us.
How we'd voice this engine
Our recommendation is a titanium valved catback.
Titanium here, stainless on a V8. The reason is in the rev limit, not in the badge. A 4.0-litre flat-six at 9,000 rpm pushes most of its acoustic energy into the upper mid and top octaves, and titanium's thinner, stiffer wall preserves that instead of rounding it off. It is also lighter, and on a mid-engined car where Porsche stripped sound deadening, removed the rear seats and deleted roughly 300 kg, every kilogram out of the tail is a kilogram that is not behind your head. The GT4 RS is the strongest titanium case in the whole Porsche range — stronger even than a 991 GT3, because the weight argument is sharper.
The factory already answered this. The standard rear pipes are titanium. If you fit a heavy stainless system you are taking a lighter, brighter factory standard and replacing it with something heavier and duller. That is a legitimate choice for a car used in the wet, but you should be choosing it, not arriving at it by default.
Keep the catless downpipe. The workshop clip shows why this car responds so well to a straight-through header run. A mid-engine flat-six with 9,000 rpm of airflow downstream does not need help on the intake side — it needs the exhaust side to stop fighting it. That decision is already made in this clip, and it was the right one.
Two ways to build this car
Route one: titanium valved catback. This is the default we would fit to a GT4 RS. The 718 GT4 RS 4.0 titanium valved catback matches the factory material logic, keeps the 2 kHz-plus character that makes a flat-six worth listening to, and saves weight over the factory steel where the car is already weight-critical. Valved, so it stays usable on a street.
Route two: SUS304 if it lives in the rain. The 718 GT4 RS 4.0 SUS304 valved catback is the same fitment in thicker, more durable steel. We would only steer you here if the car is a track toy that lives outside, or if you have heard a stainless flat-six and preferred the extra weight of it. It will not be brighter. It will last longer.
The same choice exists across the 718 line. If you came up through the 718 GT4 GTS titanium catback the material logic is identical. And if your car is the older mid-engined generation rather than the RS, the 718 982 titanium catback is the closer match. Our 991 GT3 piece makes the same titanium argument for the same reason — same engine family, same reasoning.
The honest warnings
The 718 is end of life. Porsche finished production of the current 718 series in October 2025. If you own one, you already knew. Parts availability will only get worse, not better, and that cuts both ways: it makes a car like this more collectible, and it makes waiting for a cheaper system a worse plan.
Titanium is not indestructible. It is lighter and brighter, and it is also more expensive to repair and easier to mark. Heat tint is part of the aesthetic. If that bothers you, buy the stainless and accept a quieter top end.
A catless downpipe is not free. On a mid-engined 718 the routing is tight and the heat shielding matters more than it does on a rear-engined 911. Done badly, a catless pipe costs you a heat-soaked floor. This clip shows it done properly, with shields in place. Ask for that.
These clips are not a sound test. Two of the three are filmed from a moving car. We are publishing them because they are real customer footage and because the hardware is visible, not because they are a measurement.
A question for the owners
GT4 RS owners: with a 4.0-litre flat-six sitting right behind the passenger seat and side intakes feeding it air in the cabin, how much of the driving experience is the exhaust note — and how much is the intake roar through those NACA-style ducts? Because with a good system the two merge, and at that point it stops being a car with an exhaust and starts being an engine bay you are sitting inside. We would like to hear what yours sounds like with the catless pipe and a proper rear section.
Questions we get asked about the 718 GT4 RS exhaust
Titanium or stainless for the GT4 RS? Titanium. The 9,000 rpm flat-six lives in the upper mid and top octaves, and the factory already ships titanium tips for the same reason. Stainless is defensible for durability, not for sound.
Does a catless downpipe void the warranty? It is a bolt-on accessory that leaves emissions hardware in place. That said, any aftermarket downpipe can affect your powertrain warranty position, and Porsche is not known for being relaxed about that. Keep your paperwork and check with your dealer.
Is the GT4 RS different from the GT4? Yes. The RS gets the 4.0-litre flat-six and 500 PS; the standard GT4 has a smaller engine. The exhaust is not interchangeable between them, so confirm which you have before ordering.
Will this fit the 981 or 987 Cayman? No. Those are the older mid-engined cars with a completely different rear section. We list them separately — the 981 axle-back and the 987.1 axle-back systems cover those.
HMD builds the Porsche 718 exhaust range in SUS304 and titanium, valved, catback and straight-through. Browse the catback and titanium alloy collections, or message us with your model year and which of the three clips you recognise.